Electronic animal control systems are known for confining an animal to a selected area, or to otherwise control the movement of an animal relative to a selected area. For example, such systems as are manufactured by the Invisible Fence Company of Malvern, Pa. have become a popular alternative to traditional fencing for confining animals in residential areas.
In an electronic animal control system, an antenna in the form of a wire is positioned to define the boundary of the selected area. Typically, the wire is laid underground along the perimeter of the area. The wire is connected to a radio frequency signal generator so that a radio frequency signal is radiated from the wire. A receiver for receiving and detecting the radio frequency signal is mounted upon the animal. The receiver includes a transducer, such as a speaker or a mild electric shock generator, for applying a corrective stimulus to the animal in the vicinity of the wire. Such systems, and components thereof, are described in U.S. Pat. Nos. 5,425,330; 5,435,271; 4,996,945; and 4,967,695.
A desirable application for electronic animal control systems is to confine dogs or other carnivores within an agricultural area, such as a farm or orchard, for the purpose of discouraging rodents, deer, or other herbivores from consuming crops in the area. Such agricultural areas tend to be larger than residential areas, and hence require longer boundary antennae. For example, a typical residential installation may require a boundary wire antenna of a few hundred meters, while an agricultural installation may require several kilometers of wire.
With increasing length of the antenna, however, it becomes difficult to efficiently transfer the desired radio frequency signal from the signal generator to the antenna. One difficulty is that the distributed series inductance and the distributed parallel capacitance of the antenna can cause undesirable resonant oscillation that may interfere with operation of the animal control system. Another related problem is that the series inductance of the antenna can reduce the peak current in the antenna, and hence reduce the strength of the radiated signal.
One way to counteract the problems associated with using longer boundary wires would be to provide a capacitance in series with the output terminal of the signal generator, in order to cancel the series-inductive component of the distributed reactance of the boundary wire antenna. However, because each installation of an animal control system differs from other installations in terms of wire length, geometry, and soil conditions, a single capacitance cannot be selected to compensate for the series inductance under all conditions. Consequently, it has been necessary to provide skilled installation personnel to measure the relevant electrical parameters of each installation and to custom modify the signal generator to obtain the desired compensation. Aside from being expensive and inconvenient, it is then necessary to re-tune the signal generator whenever a critical parameter of the animal control system, such as the size or shape of the area, is desired to be changed.
In view of the difficulties of custom tuning a large-area electronic animal control system, and of maintaining such a system in tune, it would be desirable to provide a signal generator for such a system that would be capable of detecting whether the antenna current is in phase with the voltage applied by the signal generator, for indicating a degree to which the voltage and current are out of phase, and for providing a phase adjustment feature for correcting any detected phase difference. Such a signal generator would desirably achieve these objectives in a manner requiring little or no special skills or training on the part of the user.